Basically a nest is a place where the eggs are laid and
young mature providing them with security, support and insulation.

Who builds?

Like most of the finches, hen canaries are the home makers although in most cases the cock co-operate in bringing material to the nest. Construction of the nest must be well timed in relation to other events in the breeding cycle, such as egg-layng. Experimental analysis has shown that this behaviour is triggered off controlled and brought to an end by a combination of interacting internal and external stimuli.

The mechanism of nest building

Nest building involves a lot of time and industry. Hundreds of trips are made carrying nesting material until the nest is in shape. They use a relatively small number of stereotype movements to weave, tuck and thread the material in order to form the structure of the nest. Canaries and many other finches use an open cup type of nest.
Hen canaries build the nest in two phases. Firstly the outer cup is constructed of nesting material provided by the breeder, and then feathers are used to line the cavity just before the eggs are laid. Nesting behaviour is stimulated by female sex hormone oestrogen which is produced under both the influence of increasing hours of daylight in the spring and by the courtship behaviour of the cock, which intensifies at this time of the year. The nest is, therefore, started and as building proceeds, stimulation from the actual nest influence the hen's choice of nest material, but in an indirect way.
With increasing levels of oestrogen in the blood, the hen commences to shed some breast feathers, leaving bare sensitive brood patches. These become highly vascular just before the eggs arrive and they will serve to keep the eggs warm at a relatively high temperature or else the embryos will fail to develop. It can well be imagined that the rough textured material will stimulate these sensitive areas at this time, causing the hen canary to change her choice of nest material to feathers to cut down the sensation and also provide a soft, well insulated interior to the nest.

Nest Sanitation

Keeping the nest clean is required to have a good survival value because it would help to keep disease and parasites in check. Egg shells and faecal sacs are removed or eaten by the parents. When the chicks are older, normally when they are seven to eight days old, the faeces are squirted beyond the rim of the nest.